In a conventional stretching structure for a chair, a groove is formed in the corner of the front side of a vertical frame, and engages with the edge which is mounted to the end of upholstery material wound in at almost 360 degrees around the outer circumferential surface, rear surface and inner circumferential surface. The end of the upholstery material is folded in a U-shape and the edge mounted to the end is engaged in a groove in an outer side surface of the frame as shown in Patent Literature 1.
A groove is formed at the back side of a vertical frame and upholstery material is wound around the front side, outer circumferential surface and part of the rear surface. The edge at the end of the upholstery material is engaged in the groove as shown in Patent Literature 2.